Andrew Emlen of Skomokawa observed a fascinating behavior last December. Here are the details as described by Andrew: A female Northern Harrier landed on a duck (possibly a wigeon, of which there were others nearby) in the pond opposite Hornstra Beach in the Julia Butler Hansen Refuge. The Harrier was belly-deep in the water as the duck struggled.
Whenever the duck struggled part of itself above the surface, the Harrier adjusted her footing in order to keep the entire duck under water. After a few minutes there was no longer any visible struggle, but the Harrier waited seven minutes before she began walking. She took a step with her free foot, then a slow, dragging step with the duck clutched in the other, and repeated this until she and the duck were on shore. Only the underside of the duck was facing me, and I couldn't see much of it other than a white belly and black vent and tail, due to the Harrier and vegetation blocking my view. The Harrier began tearing up her quarry and eating it.